He just announced plans to dramatically expand the site's goals beyond just asking and answering questions, declaring in a blog post that he hoped to build "an Internet-scale Library of Alexandria."

That's an implicit challenge to Google, which has long declared its mission to be "to organize the world's information and make it universally accessible and useful."

But D'Angelo noted in his post that the ""vast majority of human knowledge is still not on the Internet. Most of it is trapped in the form of experience in people's heads, or buried in books and papers that only experts can access."

Besides asking and answering questions, Quora allows users to write posts about topics on boards, or topical discussion forums on the site. D'Angelo's announcement suggests that Quora will be dramatically expanding such general-purpose writing tools, in competition with Twitter, WordPress, and other Web-publishing options.